While some early AIS
splitters had troubles, that was a (relatively) long time ago. Sure a splitter could fail but so could a lot of other stuff.
The arguments for a modern splitter like the one from Vesper are pretty strong:
A: As mentioned, it lets you put the AIS antenna
at the highest point substantially increasing your AIS receive and transmit range
B: The cost of a 2nd antenna
is considerably more if you include good coax (LMR-400), an antenna mount, and - if you don't like drilling holes high in the air - installation
C: The Vesper has several useful features including an amplifier to increase AIS reception
range and an LED that shows you have a good antenna connection.
Vesper Marine VHF/AIS/FM Antenna Splitter